1. Field of the Invention
This invention relates to woven bags and similar containers designed for granular and liquid substances. In one aspect this invention relates to impact resistant bags made of a woven plastic fabric. In another aspect it relates to a bag for containing explosives for use in boreholes.
2. Description of the Prior Art
Explosive bags for use in deep boreholes such as those employed in mining operations must be designed to withstand dynamic impacts. In certain types of mining operations such as coal strip mining, bags containing explosives are dropped, one at a time, in a borehole. The explosive bags are collected at the bottom of the borehole and ignited. These bags must be designed to withstand free-fall impact on the water level in the borehole or the bottom of the borehole (if dry). Premature rupture of the bag during placement in the borehole results in deficient and frequently ineffective utilization of the explosives. In boreholes containing water, impact rupture at the water level causes the viscous emulsion explosive to bridge thereby preventing passage of subsequent explosive bags. Moreover, certain explosives such as ammonium nitrate are water sensitive and are rendered inoperative if the bag ruptures or leaks prior to ignition.
The problem of premature explosive bag rupture was addressed in U.S. Pat. No. 4,369,711 and the solution proposed therein involved the use of reinforcing sleeves on the lower portion of a woven bag.
U.S. Pat. No. 4,205,611 discloses an explosive bag which comprises a laminated structure of an internal waterproof liner, an external woven support, and an intermediate oil barrier film.
Although both of these patents disclose the use of woven fabric in explosive bags, neither distinguishes between the requirements of the circumferential yarns and the longitudinal yarns in such woven fabrics. As a result, use of the woven fabrics in accordance with prior art bag structures is less than optimum, since, as will be demonstrated below, the longitudinal yarns are overly designed for the explosive bag application.